1. Field of the Invention
The present invention relates to a radiation detection apparatus and radiographic imaging system which can be used in, for example, a medial image diagnostic apparatus, a nondestructive inspection apparatus, and an analysis apparatus using radiation.
2. Description of the Related Art
In recent years, as a technique for manufacturing a liquid crystal display panel using a thin-film transistor (TFT) makes advance, the sizes of both the panel and the screen of its display unit increase. This manufacturing technique is applied to a wide area sensor including a photoelectric conversion element or a direct conversion element which directly converts radiation such as X-rays into a charge, and a switching element such as a TFT. An area sensor including a photoelectric conversion element is often used in the field of radiation detection apparatuses such as a medical X-ray detection apparatus in combination with a scintillator which converts radiation such as X-rays into light such as visible light.
The pixel structures of the radiation detection apparatuses are generally classified into two types: a planar type in which a conversion element and a switching element are located on the same plane, and a stacked type in which a conversion element is located above a switching element. The former pixel structure can simplify the manufacturing process because this structure can be obtained by forming a conversion element and a switching element in the same semiconductor manufacturing process.
In contrast to this, the latter pixel structure can include a conversion element formed to have an area per pixel larger than that in the planar type because this structure is obtained by locating the conversion element above a switching element. This allows the radiation detection apparatus to obtain a large signal and therefore to have a high S/N ratio, that is, high sensitivity. Japanese Patent Laid-Open No. 10-123253 and 10-511817 describe details of radiation detection apparatuses of the stacked type as mentioned above.
In a radiation detection apparatus, as the parasitic capacitance of a signal line increases, the amount of noise, in turn, increases. Under the circumstance, to improve the sensitivity of even a radiation detection apparatus of the stacked type, it is important not only to improve its numerical aperture but also to reduce noise, that is, reduce the capacitance added to a signal line. To attain this, the interlayer insulation film is desirably thick. Japanese Patent Laid-Open No. 10-123253 and PCT(WO) 10-511817 describe details of an interlayer insulation film having a large thickness.
On the other hand, from the viewpoint of ensuring a given coverage of the sensor film, the height of a contact hole to connect the conversion element and the switching element is preferably low, that is, the thickness of the interlayer insulation film is preferably small. In addition, to leave a sufficient margin in the layout of each element and interconnection, both the thickness of the interlayer insulation film and the hole diameter are desirably small. However, in such an arrangement, the image obtained when the interlayer insulation film has a thickness as small as, for example, 500 nm is more likely to have unevenness, which deteriorates its quality, than that obtained when the interlayer insulation film has a large thickness.